Zoom lens system

Abstract

A zoom lens system includes, in order from an object, a first lens group having positive power, a second lens group having negative power, a third lens group having positive power, a fourth lens group having positive power, and a fifth lens group having positive power. Upon zooming from a wide-angle end state to a telephoto end state, the first and fifth lens groups moves with respect to the image plane, the second lens group moves at first to the image and then to the object, and the third and fourth lens groups move to the object such that a distance between the first and second lens groups increases, a distance between the second and third lens group decreases, a distance between the third and fourth lens groups decreases, and a distance between the fourth and fifth lens groups increases. Given conditional expressions are satisfied.

1. A zoom lens system comprising, in order from an object:
 a first lens group having positive refractive power; 
 a second lens group having negative refractive power; 
 a third lens group having positive refractive power; 
 a fourth lens group having positive refractive power; and 
 a fifth lens group having positive refractive power, 
 wherein when a state of lens group positions varies from a wide-angle end state to a telephoto end state, the first lens group moves with respect to an image plane, the fifth lens group is fixed with respect to the image plane, a distance between the first lens group and the second lens group varies, a distance between the second lens group and the third lens group decreases, a distance between the third lens group and the fourth lens group decreases, and a distance between the fourth lens group and the fifth lens group increases, and 
 the following conditional expression being satisfied:
   10.0 <f 1 /fW <14.0 
 
 where fW denotes the focal length of the zoom lens system in the wide-angle end state and f 1  denotes the focal length of the first lens group. 
 
   
   
     2. The zoom lens system according to  claim 1 , wherein focusing from infinity to a close object is carried out by moving the fifth lens group to the object. 
   
   
     3. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   4.0 <f 5 /fW <9.0 
 where f 5  denotes the focal length of the fifth lens group. 
 
   
   
     4. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   7.0 <f 1 /|f 2|<11.0 
 where f 2  denotes the focal length of the second lens group. 
 
   
   
     5. The zoom lens system according to  claim 1 , wherein the third lens group is composed of, in order from the object, an aperture stop, a front lens group, and a rear lens group, the front lens group is composed of a cemented lens constructed by, in order from the object, a negative meniscus lens having a convex surface facing to the object cemented with a positive lens having a convex surface facing to the object, and the rear lens group is composed of a cemented lens constructed by, in order from the object, a positive lens having a convex surface facing to the object cemented with a double concave negative lens. 
   
   
     6. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   1.0 <f 3 a/f 3<1.5 
 where f 3  denotes the focal length of the third lens group, and f 3   a  denotes the focal length of the front lens group. 
 
   
   
     7. The zoom lens system according to  claim 1 , wherein the following conditional expression is satisfied:
   0.10 <fW/f 3 a <0.20 
 where f 3   a  denotes the focal length of the front lens group.